Theory of Raman response of a superconductor with extendeds-wave symmetry: Application to the iron pnictides

Abstract

We argue that Raman study of Fe-pnictides is a way to unambiguously distinguish between various superconducting gaps proposed for these materials. We show that ${A}_{1g}$ Raman intensity develops a true resonance peak below $2\ensuremath{\Delta}$ if the pairing gap has ${A}_{1g}$ symmetry in the folded Brillouin zone $(\ensuremath{\Delta}(k=0)=\ensuremath{\Delta},\ensuremath{\Delta}(\ensuremath{\pi},\ensuremath{\pi})=\ensuremath{-}\ensuremath{\Delta})$. No such peak develops for a pure $s$-wave gap, a $d$-wave gap, and an extended $s$-wave gap with $\ensuremath{\Delta}(\mathbf{k})=\ensuremath{\Delta}\text{ }\text{cos}\frac{{k}_{x}}{2}\text{cos}\frac{{k}_{y}}{2}$. We show that the peak remains quite strong for the values of interpocket impurity scattering used to fit NMR data.